Transitions, or connections, between a circuit and e.g. a waveguide or an antenna, are needed for many different applications, e.g. within microwave or millimeter wave technologies etc. Particularly due to the increasing demand for high-speed wireless links, e.g. for ultra-fast mobile Internet, high resolution automotive radar links, Gbit/s data and video links, accurate imaging devices for medical and security applications etc. it is attractive to be able to use the millimeter, or the sub-millimeter, wave frequency region, since in these frequency regions, larger frequency bandwidths are available. Thus, the use of high frequencies is steadily gaining more interest.
For example, electronically steered antennas in an antenna array system based on e.g. mm-wave technology have an enormous potential, being capable of multiple instantaneous beams, each of which corresponding to a relatively large antenna aperture area providing high receiving sensitivity or a large antenna gain. However, such systems are complex and high costs are involved with complex antenna array systems employing many antenna elements. At millimeter-wave frequencies it becomes possible to combine antennas with integrated circuits in a single process since the size of the antennas is reduced to a fraction of a millimeter, allowing them to be placed on a carrier together with an integrated circuit (IC). This reduces the fabrication costs and time, and the antennas are smaller than dielectric-free antennas.
Several problems are associated with transitions between e.g. a package comprising a high-frequency circuit and a waveguide port or an antenna. A waveguide transition generally converts its dominant waveguide mode to a microstrip or coplanar transmission line mode.
Direct ridge-to-transmission line connections have been proposed, but suffer from drawbacks, particularly from a manufacturing point of view, since the circuit may easily break.
For a connection between a transmission line and a chip (circuit) a bond-wire or a flip-chip connection has been used. Such a connection contributes with a substantial reactance at high frequencies, causing extra losses and reduction in the achievable bandwidth. Another disadvantage in using bond-wire connections at high frequencies is that bond-wires may lead to impedance mismatch, are inductive and hence limit the bandwidth and the bond-pad contact area of the circuit becomes very small at high frequencies and bonding often destroys the high-frequency pad, thus affecting the yield. Bond-wires may further produce spurious radiation and may excite cavity modes when packaged. Moreover, e.g. for antennas, the substrate on which the antennas are located will be lossy at millimeter-wave frequencies, which means that e.g. the antenna radiation efficiency is reduced. A low radiation efficiency, however, is not acceptable for systems requiring high power efficiency, or systems handling high powers. For example, in communication systems high SNR (Signal-to-Noise Ratio) it is of utmost importance to allow the use of higher-level modulation schemes maximizing the data rate. Thus, such known solutions concerning antenna/waveguide-circuit transitions involve the drawbacks of the performance being degraded due to the use of RF-bond wires, as a result of which packaging problems arise, and e.g. resonances occur, and antennas and transmission lines suffer from high losses.
Flip-chip connections also suffer from several disadvantages. Due to the lack of a carrier, they cannot be easily replaced and they are not suitable for manual installation. Still further they require very flat mounting surfaces, which often is difficult to arrange, and sometimes difficult to maintain as the boards are heated and cooled. Further, the short connections are very stiff, so the thermal expansion of the chip has to be matched to the supporting board or the connection may crack. The underfill material acts as an intermediate between the difference in Coefficient of thermal Expansion of the chip and the board.
Connections between a circuit and a transmission line based on flip-chip connections also involve large alignment problems, and misalignment may lead to the integration being ruined.
WO 2014/154232 discloses a transition between an SIW (Substrate Integrated Waveguide) and a waveguide interface. However, contact is needed between the metal waveguide and the SIW structure on two sides, requiring soldering or similar. Moreover the structure requires a 90° non-planar setup, which is disadvantageous for several reasons.
US 2014/0091884 shows a transition between an SIW and an air-filled waveguide, which also requires contact between the metal waveguide and the SIW structure on two sides. In addition, a tapering substrate is required which is disadvantageous for fabrication reasons.
In all known devices, replacement of the entire transition is needed if the circuit is damaged.
Thus, several problems are associated with the provisioning of a transition between a circuit, passive as well as active, and a waveguide or an antenna, and, so far, no satisfactory solutions have been suggested.